云凝结核对南京及周边地区夏季暴雨影响的数值模拟

Numerical simulation on impact of cloud condensation nuclei on summer rainstorm in Nanjing and its surrounding areas

利用WRF3.8.1模式,采用Thompson云微物理参数化方案,对南京2014年6月初的一次暴雨过程进行模拟;设置多组数值试验,从中选取清洁和严重污染两组试验,对比分析低、高云凝结核浓度对此次降水的影响。结果表明:1)Thompson方案对此次降水过程具有一定的再现能力,但对24 h累积降水量的模拟整体偏低,且随云凝结核浓度的上升,累积降水量增加。较高的云凝结核浓度有利于强降水中心强度增强、降水范围扩大,而对较弱降水中心则有相反的影响。2)云凝结核浓度的增加将抑制云滴向雨滴的转化,使更多云滴被输送到对流层中层,对流层低层的暖云过程被抑制。3)云凝结核浓度的增加使对流层中层的过冷云水增加,促进过冷云水向霰的转化,也促进雪的淞附过程,这有利于冷云过程的发展。4)云凝结核浓度的增加对暖云过程具有负反馈作用,对冷云过程具有正反馈作用。

WRF3.8.1 model was chosen to simulate a rainstorm process in Nanjing in early June 2014 with Thompson cloud microphysics parameterization scheme.The effects of cloud condensation nuclei(CCN)concentration on the rainstorm were compared by two numerical experiments,which represent the high and low CCN concentrations,respectively.Results show that:(1)Thompson scheme can reproduce the rainstorm process to a certain extent,but the simulation of 24 h cumulative precipitation is generally low,and the cumulative precipitation increases with the increase of CCN concentration.The higher CCN concentration is beneficial to the enhancement of heavy precipitation centers and the expansion of heavy precipitation range,while it has the opposite effect on the weak precipitation centers.(2)The increase of CCN concentration will inhibit the transformation of cloud droplets to raindrops,more cloud droplets will be transported to the middle troposphere,and the warm cloud process in the lower troposphere will be inhibited.(3)The increase of CCN concentration increases the supercooled cloudwater in the middle troposphere,promotes the transformation of supercooled cloudwater to graupel,and promotes the riming process of droplets onto snow,which is conducive to the development of cold cloud process.(4)The increase of CCN concentration has negative feedback effect on warm cloud process and positive feedback effect on cold cloud process.